The invention relates to an electronic circuit, particularly for and in a mobile transceiver, which has a digital circuit section and an analog circuit section connected to the digital circuit section.
It is known to use in radio frequency transmitting and receiving circuits phase-locked loop (PLL) circuits which control the phase and, if necessary, also the frequency of the transmitter and/or receiver to a desired value. For this purpose, frequently a voltage-controlled oscillator (VCO) generating the transmitting or receiving carrier frequency is controlled to the nominal frequency by the voltage applied to it. To achieve a sufficiently large control range, a correspondingly high control voltage swing is desirable which needs a correspondingly high supply voltage. On the other hand, the remaining signal processing, for example in a mobile transceiver, largely takes place at a digital level. At this level, low supply voltages of, for example, 2.7 V are increasingly used for reducing the power dissipation, temperature generation and the like. In the radio-frequency section, however, such low supply voltages lead to only low controllability so that the tuning range is restricted.
In U.S. Pat. No. 4,598,217, a phase/frequency detector for a phase-locked loop is shown. A digital circuit section at the input end is coupled to an analog circuit section at the output end. The digital circuit section has a supply voltage of 5 V. The analog circuit section has another supply voltage. To convert the signals to be transferred from the digital circuit section to the analog circuit section, a level converter is provided. The level converter contains current sources and current balancing circuits.
In Patent Abstracts of Japan, Vol. 1996, Nr. 10, Oct. 31, 1996 (JP-A-08-162951), a phase-locked loop is shown in which a charge pump converts output signals of the phase comparator to the loop filter. In U.S. Pat. No. 5,623,523, a further phase-locked loop is shown in which digitally provided upward-and downward-pumping signals drive a charge pump that is driven by a voltage boost network that is supplied by another supply voltage. The charge pump controls a loop filter.
It is accordingly an object of the invention to provide an electronic circuit, particularly for a mobile transceiver, which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is distinguished by good operability of the digital and analog circuit section.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic circuit. The electronic circuit contains a digital circuit section outputting an activation signal, and the digital circuit section has a selection device for generating selection signals. An analog circuit section is connected to the digital circuit section and receives control signals, including the activation signal and the selection signals, from the digital circuit section. The analog circuit section contains a common output, and at least two controlled current source circuits having inputs, current outputs connected to one another at the common output, logic elements connected to the inputs, and level converters connected to the logic elements. The selection device of the digital circuit section generates the selection signals for selecting at least one of the controlled current source circuit to be activated. The selection signals are received at the inputs of the controlled current source circuits and are transmitted to the logic elements followed by the level converters for generating switching signals for controlling the current outputs of respective ones of the controlled current source circuits. A reference current generator is connected to the controlled current source circuit. The reference current generator receives and is controlled by the activation signal output by the digital circuit section. The reference current generator has an input receiving the activation signal, a further level converter coupled to the input, and at least two reference current branches coupled to the further level converter. The reference current generator converts the activation signal using the further level converter and generates, by use of the at least two reference current branches, reference currents fed to the controlled current source circuits. A first voltage supply is connected to the digital circuit section and supplies a first voltage. A second voltage supply is connected to the analog circuit section and supplies a second voltage being set to a higher potential level than the first voltage.
In the invention, different supply voltages are provided for the digital circuit section and the analog circuit section so that advantageous supply voltage levels can be separately preset, for example 2.7 to 3 V for the digital circuit section and 5 V for the analog circuit section. Since the amplitudes of the control signals fed from the digital circuit section to the analog circuit section can only be varied within the extent of their supply voltage, level converters which transform the control signal voltage level to the control level needed by the other circuit section are preferably provided at the input or output of the digital and/or analog circuit section.
In an advantageous embodiment, the analog circuit section contains a controlled current source circuit preceded by a reference current generator that can be switched on and off by an activation signal supplied by the digital circuit section. The activation signal is transformed to a higher level range of the voltage supply of the analog circuit section by a level converter. The output of the current source circuit is preferably connected to a control voltage generating unit for generating the control voltage for the frequency control of a voltage-controlled oscillator which is to be controlled locked in frequency and/or phase. The control of the voltage-controlled oscillator can thus be operated with the higher level swing of the voltage supply of the analog circuit section and in consequence a wide control range can be obtained. The control voltage generating device is preferably a loop filter with a capacitance to be charged and discharged in accordance with the desired control voltage value. The phase comparator or phase/frequency detector comparing the oscillator output signal with a predetermined reference signal is then preferably a component of the digital circuit section.
The control voltage inputs of the controllable current source circuit are preceded by level converters so that the control signals supplied from the digital circuit section are transformed to the higher voltage level range of the current source circuit.
The analog circuit section contains a number of selectively selectable controllable current source circuits that are connected to a common current output terminal. In this configuration, the current source circuits can be selected by one or more selection signals so that the current intensity in each case currently fed to the current output terminal is selectable.
The reference current generator contains a number of reference current branches by which reference currents can be fed to the individual current source circuits. The level converter disposed before the reference current generator is thus utilized several times, since a single level converter is used for controlling the activation of a number of reference current branches. This reduces the necessary circuit expenditure in spite of the possibility that is offered of being able to feed a number of current source circuits at the same time.
All reference current branches can be switched on and off by one or two electronic switches connected to the level converter so that the circuit expenditure needed overall for this is low.
The level converters preferably contain an input branch which is connected to the lower supply voltage and the output potential of which is switched over by the control switching signal supplied at the input from the digital circuit section. This input branch is connected to a conversion branch connected to a high supply voltage so that the switching signal level is switched between the ground potential, which is common to the two branches, and the high voltage potential.
The circuit according to the invention is used, in particular, in hybrid (analog and digital) phase and/or frequency controllers for radio-frequency oscillators, preferably in mobile transceivers, but can also be used in other systems, achieving the advantages listed above.
In accordance with an added feature of the invention, the level converters and/or the further level converter transforms to a higher level one or more of the signals generated by the digital circuit section.
In accordance with an additional feature of the invention, a control voltage generating device is connected to the common output. The digital circuit section has a detector being either a phase detector or a phase/frequency detector. The control voltage generating device is a loop filter used for generating a control voltage for a voltage-controlled oscillator which is controlled to be at least one of phase-locked and frequency-locked and an output signal of which is fed to the detector contained in the digital circuit section.
In accordance with another feature of the invention, the further level converter has an output, and the reference current generator contains at least one electronic switch connected to the reference current branches for switching off all of the reference current branches at a same time. The electronic switch is connected to the output of the further level converter.
In accordance with a further feature of the invention, the level converters and/or the further level converter contains an input stage connected to the first voltage supply and receives the first voltage and one of the signals generated by the digital circuit section, and a conversion and output stage connected to the input stage. The conversion and output stage is connected to the second voltage supply and receives the second voltage. The conversion and output stage outputs an output voltage switched between a common ground and the second voltage in dependence on the one signal applied to the input stage. The input stage and the conversion and output stage are both connected to the common ground.
In accordance with a concomitant feature of the invention, the analog circuit section is a radio-frequency section and the electronic circuit is a phase-locked loop for a mobile transceiver.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electronic circuit, particularly for a mobile transceiver, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
FIG. 1 is a diagrammatic block diagram of an exemplary embodiment in the form of a phase-locked loop according to the invention;
FIG. 2 is a block circuit diagram of a current source configuration in the phase-locked loop;
FIG. 3 is a circuit diagram of a reference current generator preceded by a level converter;
FIG. 4 is a block circuit diagram of a current source circuit preceded by level converters;
FIG. 5 is a circuit diagram of the level converter; and
FIG. 6 is a circuit diagram of the current source circuit.